[Brahms-dev-l] Re: FS tracking efficiency with the reference method.

Howdy Peter.

Peter H.L. Christiansen wrote:
> Yes it is a bit strange/unphysical with the discontinuities between 100% 
> and 80%. I believe that Pawel has once showed that the efficiencies works 
> in the sense that FFS and FS is similar with efficiencies. I am also 
> convinced that it works since Djamel and I have compared FS to FFS and 
> different FS/FFS settings to each other where the efficiencies were quite 
> different and found good agreement.

Well, I'm not convinced by this argument. It may very well be that both 
FS _and_ FFS effiencies are wrongly calculated. The values of 100% 
effiency show up also in T1 and T2. So you could very well have nice 
agreement in e.g. efficiency corrected FS and FFS spectra and both being 
wrong.

> So likely for some reason we don't quite understand the tracking "works
> better" in some part of the detector than others or the statistics is
> low or .... It is at least also somehow clear that the 3d histogram is too 
> big for the low number of tracks that makes it all the way through the 
> FS, and maybe you could reparamatrize this, summing over the top 0-20% 
> and summing over fx the coordinate in a detector to get an efficiency 
> that you can apply track by track. 
> 
> What Djamel and I did was to calculate the average tracking efficiency as
> a function of momentum (a profile of the single track efficiencies) and to
> use that for the correction (actually using the average where the counting
> statistics was low) - this is at least be continous. I think we got the
> same results no matter what we did, but it makes it a lot easier to
> understand what you do.

That's what I'm doing too. But what bothers me is the dependence on 
momentum, i.e. where there is significant negative slope in the 
efficiency as function of momentum, as shown in some of the plots in [1].

Best wishes from
Jens Ivar

[1] http://www.ift.uib.no/~jens/trackingefficiency
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